% drop(+L1,+N,-L2).
% ?- drop([a,b,c,d,e,f],3,X).
% X = [a,b,d,e].

drop([],_,[]):-!.
drop(L1,N,L2):-
    drop(L1,N,N,L2,[]).
    
drop([],_,_,L2,L2):-!.
drop([X|T],Counter,N,L2,Acc):-
    Counter \= 1, !,
    Counter1 is Counter - 1,
    append(Acc,[X],Acc1),
    drop(T,Counter1,N,L2,Acc1).
    
drop([_|T],Counter,N,L2,Acc):-
    Counter == 1, !,
    drop(T,N,N,L2,Acc).